Method of consolidating a formation using a heater within a liner which is thereafter destroyed



Dec. 29, 1964 T. o. ALLEN ETAL 3,163,218

METHOD OF' CONSOLIDATING A FORMATION USING A HEATER WITHIN A LINER WHICHIS THEREAFTER DESTROYED Filed March 14, 1960 4 Sheets-Sheet l la t: leI6 FIG.3

Thomas O. Allen John E. Ortloff Bertram T. Willman Inventors BY -ma...)t. Qui. Alorney Dec. 29, 1964 T. o. ALLEN ETAL.

METHOD OF CONSOLIDATING A FORMATION USING A HEATER WITHIN A LINER WHICHIS THEREAFTER DESTROYED 195o 4 Sheets-Sheet 2 Filed March 14.

FIG. 5

FIG. 4

Thomas O. Allen John E. Ortloff Bertram T. Willman Y Invenors` By e.(2....),

Attorney Dec. 29, 1964 T. o. ALLEN ETAL 3,163,218

`METHOD 0F CONSOLIDATING A FORMATION USING A HEATER WITHIN A LINER WHICHIS THEREAFTER DESTROYED Filed March 14. 1960 4 Sheets-Sheet 5 FIG.6

Thomas O. Allen John E. Orloff Bertram 'I'. Willman Inventors By 5AOTney Dec. 29, 1964 T. o. ALLEN ETAL 3,163,218

METHOD OF cONsOLIOATINO A FORMATION usING A HEATER WITHIN A LINER wHIcHIs THEREAFTER OESIROYEO Filed March 14, 1960 4 Sheets-Sheet 4 FIG.7

Thomas O. Allen John E. Ortloff Bertram T. Willman ,Invenors By MH...)E. QLML Attorney oil in contact therewith.

nited States Patent O 3 163 218 Martino or coNsrLrnArrNG A FoniviarrcrlUSING A HEATER WlTI-HN A LINER WHCH iS THEREAFER DESROYED f rhornasAllen and .lohn E. Grtlo, Tulsa, kla., and Bertram 'I'. Wilman, Union,NJ., assignors to Jersey Production Research Company, a corporation ofDelaware Filed Mar. 14, 1960, Ser. No. 14,905 4 Claims. (Ci. 1661-25)The present invention relates to methods for consolidating subsurfacereservoirs in the vicinity of oil wells, gas wells and similar boreholesand more particularly relates to an improved thermal consolidationprocess wherein heat is applied to a reservoir in order to coke lnstillV greater particularity, the invention relates to a thermalconsolidation process wherein an expendable liner is positioned in thewellbore, heat is applied to the reservoir through the liner, and theliner is thereafter at least partially destroyed in order to restorecommunication with the reservoir.

Many subsurface oil and gas reservoirs are located in formations made upof unconsolidated or loosely consolidated sand particles. When a Welldrilled into such a reservoir is placed on production, the uids enteringthe wellbore carry entrained sand particles with them. These particlesvtend to settle in the wellbore and clog it, necessitating workoveroperations at frequent intervals. Particles which do not settle in thewellbore and instead are entrained in fluids pumped to the surface causeexcessive wear and erosion of pumps, tubing and other apparatus. Erosionof sand from the formation by the producing fluids may lead toundermining about the wellbore and cause the subsidence of overlyingstrata. When this occurs, the tubing or casing may be bent or, in somecases, completely collapsed. This sometimes necessitates abandonment ofthe well, or makes it necessary to perform an expensive sidetracking andredrilling operation. Subsidence of the overlying strata may permit theentry of foreign uids into the producing reservoir or, particularly inthe case of gas wells, permit substantial quantities ofthe reservoiriiuid to escape int higher reservoirs outsidefthe .producing zone.

A Vnumber of methods designed to prevent the inux of sand particles intowells completed in unconsolidated reservoirs and thus alleviate thedifculties outlined above have been suggested in recent years. Aparticularly attractive method involves heating the-unconsolidated zone.

about the wellbore to temperatures -suiicientto coke oil in thevformation and cement the particles together. Experimental work and fieldtest have shown that this method can result in a highlyV permeable,well-consolidated area about the wellbore. There are certain problemsVwhich must be overcome, however. The presence of gate into light endswhich are carriedupwardly bythe convection currents and 'heavy'components which settle about the heating unit.V 'Ihe heavy constituentsof theoil generallycoke'rnuch more rapidly than do'the lighter materialsand hence a thick layer of coke tends to form about the heater near thebase of the producing zone.

This may cause the heaterto become `stuck inthe wellbore.

thermal consolidation process which circumvents the difflculties setforth above. In accordance with the invention, it has now been foundthat the use of an expend- The present inventionproviders a new andimproved "ice,

able liner in the wellbore opposite the zone to be con-`V solidatedpermits the application of heat to the' reservoir from within the linerwithout the establishment of convection currents in the wellbore andwithout dangerl ofV cementing the heater in place. The heat applied `tothe. reservoir can be controlled to better advantage so that in mostcases the time required for coking is greatly reduced. The use of'aliner which can at least in part be destroyed by chemical, thermal orother methods after coking has been completed, without injuring theconsolidated structure, permits uids to be produced from the formationwithout` diiiiculty.

The liner employed in carrying out the process of the invention may beconstructed of a variety of different metals having melting points inexcess of the coking temperature. Metals which can readily be destroyedby treatment with chemical Vagents without damaging the consolidatedformation surrounding the wellbore are generally preferred.Representative examples of such metals and chemical treating agentswhich rapidly attack them are shown in the following table.

Metal Chemical Agent Aluminum 1 N Sodium Hydroxide.

35% Hydrochloric Acid.

% Propionic Acid.

Mixed 50% Suliurie Nitric Acid.

15% Nitric Acid.

15% Hydrochloric Acid.

15% Sulfuric Acid.

55% Nitric Acid.

55% Nitric Acid.

15% Ammonium Hydroxide.

55% Nitric Acid.

40% Hydrochloric Acid.

15% Ammonium Hydroxide.

25% Phosphoric Acid.

Acid-50% Magnesium 25% Nickel-75% Iron Alloy Copper Brass Nickel Bronze1t will be understood that the above metals and chemical agents aremerely representative and that other metals, other agents and otherconcentrations may be e ployed in carrying out the invention.

In addition to metals which are subject to chemical attack, metals thatmelt at temperatures slightly higher than the coking temperature may beutilized for carrying out theV process of the invention., By rapidlyincreasing the wellbore temperature following completion of the cokingoperation, the -metallicliner can be meltedtoV complete the well.Suitable metals and their 'melting points include the following.

. Crudeoils can readily be coked at temperatures be- `tween about 600 F.and about 1500 F. The optimumYV coking temperature will depend somewhatupon the com?, position of the oil and the pressure conditions in theborehole. As indicated by the `above table,Y a variety; of metalsandrmetal alloys melting at temperatures between about 1000 F. and about1650 F.'areY available andfrnay be utilized in the practice of theinvention. .The particular metal employed will, of course, dependuponthe -coking A temperature utilized.'

The coniiguration of the liner used in carrying out the process of theinvention will depend in part upon the metal employed and in part `uponthe method, chemical or thermal, to be used to render the linerpermeable v'following the coking operation. Because many metals otherwise particularly suitable for purposes of the invention lose muchof'their strength at temperatures in the coking range, it is generallypreferred to'employ an inner perwith` an outer layer o r sheath of themetal to be chemically or thermally removed. In other cases, a linercontaining one or more plugs lor sections of metal which may be removedby chemical or thermal means will beV preferred. In still otherinstances, however, ahornogeneous liner may be used. Q

In carrying out the process of the invention, a liner which can betotally or in part removed by chemical or thermal means is rst loweredinto the wellbore opposite the unconsolidated formation. The wellboremay contain casing vwhich has been perforated opposite an unconsolidatedproducing zone or instead may be open opposite the unconsolidated zone.YIn a wellbore of the rst type, the liner will normally bev suspended atthe lower end of a string of producing tubing and a heatresistant packerwillV be'placed between the casing and 'tubing above the liner. YIn awellbore open opposite the unconsolidated formation, the liner may beconnected to and supported by the lower .end of the casing.` Afterthe'liner has been set in place,f-a borehole heater of the."

chemical, electrical or combustiontype is lowered into ,the liner. Heatis then applied to thek reservoir through the linerY wall.` Thelighterlconstituentsof `theoil sur.-

rounding the linerare vaporized by theheat and'for'cedY into theformation.V` The heaviercomponents which remain in the formation in thearea adjacent the liner are converted into coke. The coking which thusoccurs con- Y solidates the formation. 1After coking has been com-Y Ypleted, theliner is at least in part destroyed by Vrapidly increasingthe wellbore temperature or by removing the heater and introducing achemical agentinto theA liner.V

FIG. represents in vertical section a wellbore open opposite anunconsolidated producing zone wherein an Y expendable liner has beenconnected to the lower end .-forated liner of alloy steel or ceramicmaterial provided Y l Y Yof the casing and cemented in place;

FIG. 2V is a vertical section through the wellbore of FIG. l after thecementing plugs have been removed and. the heater has been suspendedinside the liner to start Vthe coking operation;

FIG. 3 depicts in verticalV section the wellbore shown in FIGS. 1 and 2aftercoking has been completed and4 Y the liner has been destroyed.

forated Ywellbore containing an expendable liner and Y FIG. 4 is avertical section through a cased and -perheater useful in the practiceof the invention;

FIG. 5 is a partialview of the wellbore of FIG. 4 showing'an alternatemethod for closing olic the lower end of the liner employed in theVpractice of the invention;

' FIG. 6 illustrates in vertical section a wellbore con?- taining aslottedliner ittedwith an yexpendable outer sleeve; and,

FIG. 7 is a vertical section through a wellbore containing la slottedliner provided with plugs of a lower` melting point metal moresusceptible to attack by chendv cal agents than the base metal oftheliner.

Turning now to FIG.,1, reference numeral 11 designates a wellboredrilled into an unconsolidated oil-pro'- ducing reservoirV beneath theearths surface. has been installed in the upper part of theA wellboreabove unconsolidated zone 13. Collar 14,'attached to the lower end oftheY casing before it is lowered into place, supports cementing plug 15of brass, aluminum orY other drillable material and cementing basket 16carried on the Voutside of the casing.V A cement basket of the typesuitable for this purpose is shown on p. 2212 ofthe l 958-59`.CompositeVCatalog and can be furnished by Halliburton Oil Well Cementing; Company,Duncan, Oklahoma. Ports` If heat is used to meltthe liner,1the moltenmetal'will ilow` into the bottom of the wellbore and solidify after theheater has been removed.V Where a slotted 'liner containing fusibleplugs is employed, Va gas or other fluid can often be injected into theWellin Yorder to force the .metal out into the .formation after it hassoftened. If a Vchemical agent is usedfto dissolve at least part of theliner, it` may be pumped down the well casingor tubingv for insteadmaybe injected'Y through a corrosion-resistant hose or string` of.tubin'glow'ered intoY the.A lwell lforY that purpose. Many acids andbases Ysuitablejfor use inthe practicefof the invention have littleor-norelect`upon alloy steel Well tubing and casing and do not requirethat particularV precautions be taken; It is frequently .advis-y able,however.. to inject a neutralizing'agent after/.the` liner hasbeenldissolved'in order to prevent corrosion of the well maycomeintocontact. Y i The process Vof. the invention is Yparticularly useful as ameans for completing *wellsY Y drilled intof unconsolidated equipment'witlrwhich the initialfluids producedfrom oil-producingreservoirsbutmayalso beiutilized mires- Vshaped torincrea'seits'fresistance 'to external pressure. In Vlieu of a continuouslinerhaving a rounded` bottom` as` shown in FIG.1,'a liner consisting ofametallic sleeve *i Vfitted with a suitable capk or` plug at its lowerendjmay be utilized. The collar 14 may be an integral part of theervoirs which contain little or no' oil'. YIt is sometimes de-Y 17 abovethe cementing'plug extend through thecasing wall to Vpermit the. passageof cement into the annular space between the casing and borehole wallabove the basket. .Upper plug 18Y has been provided above the cement 19within the casing to facilitate pumping of the cementdownwardlytherein.` A plug of this type is also readily available fromthe Halliburton Oil Well Cementing Company in Duncan, Ok1homa, and isshown on page 2211 of the 1958-19'59 Composite catalog. As

shown'in FIG. 1, the cement has'beencirculated down` thezcasing and upthe annular space and has been allowed to set.V Y l f Y Liner 20 ofbrass or a smilarmetalwhichcan be fused at temperatures somewhat abovethe'cokingY tem` per'ature'or dissolved with an acidicfor basic reagentis attached to the lower endf; of collar 14 below cementing plug 15. Theliner `n1ayibe corrugated or otherwise liner if desired.

. After thecasing and liner 20 have been installed in the j wellbore asdiscussed in the preceding paragraph," the cementingplugs 15 and 18 andthe ement remaining; therebetween are drilledr out inthe conventionalmanner. Anelectrical heaterV 21 supported by an varmoured cable 22 orother suitable heating-device is the'nlowered"into-V the liner as shownin FIG'. 2 of the drawing. Ihe'heater isturned onand heat is transmittedto the formation by conduct /ion' and radiation. Thermocouples, notshown, maybe installed on Hthe innerwallof thevline'r for pur- `poses oftemperature control, if .i desired. Heat reaching oil in the wellboreoutside the -liner and in the surround-` ing formation results invaporization'of Vthe lighter con#` Vstituents ,of the toil. V'I hevaporized materials are forced finto the formation, leaving theheavier'components of the oil behind. These` areY convertedl'intocokeV23'which Casing 12 'v animate` serves to bond together the particlesmaking up the formation. The liner and the cement between the casing andformation wall prevent excessive heat losses, gravity segregation andother difliculties which might otherwise arise in the coking process.The time required for the formation of sufficient coke to consolidatethe unconsolidated zone will depend largely upon the characteristics ofIthe oil in the reservoir and the coking temperature utilized. Thecoking rate under a particular set of conditions can readily bedetermined in advance by coking samples of the oil at the surface underVsimulated wellbore conditions.

Upon completion of the 'coking operation as described above, the linershown in FIGURES l and 2 is at least in pant destroyed by treating itWith nitric acid or a similar reagent. A tube of Teon or othercorrosion-resistant material may be inserted in the wellbore to conveythe acid or other reagent into the lining in the event that a reagenthighly corrosive to steel casing is used. The elevated temperature ofthe linerl following the coking operation accelerates reaction betweenthe liner metal and the reagent and results in rapid destruction of theliner.

Tests have shown that petroleum coke formed in the wellbore in themanner described herein is relatively inert with respect to acids andbases and that permeability is not. appreciably alected during thedestruction of the liner. A neutralizing reagent can be pumped down thewellbore after the liner has been destroyed in order to counteract anyreagent which may have contacted the casing or may remain in the bottomof the well. 'I'he wellbore following destruction of the liner is shownin FIG. 3 of the drawing.

Reference is now made to FIG. 4 of the drawing which depicts a cased'andperforated .wellbore containing an expendable liner and anelectrical-heater useful in the practice of the invention. Casing 26extends below the unconsolidated producing zone 27 `and has beencemented in place in the conventionalmanner, the cement being designatedby reference numeral 28. Perforations 29 penetrate the casingrandjcementopposite thev producing zone. In the practice of the invention'in such awellbore, an expendable liner 30 of aluminum or a similar metal islowered into the wellbore and held in place opposite the producing zoneby means-of a conventional packer or other anchoring Vdevice 31. Atypical liner hanger and packer assemblypis shown on page 4848 of the1958-59 Composite Catalog and is available from the Texas Iron Works,Inc., of Houston, Texas. If a packer" is employed, it will preferablybeconstructed of asbestos or otherheat resistant material. Aconventional packer of rubber or the like positioned a suicient distanceabove the perforated section of thecasing to avoid damage due to hightemperatures may be used in some cases, however. After the liner hasbeen installed, and the hole bailed substantially dry, electrical heater32 is lowered into'place opposite the unconsolidated formation and isused to coke oil present therein. Following they coking operation, theheater may be withdrawn and the liner iilled with a 'chemical agent toeffect its destruction. The chemical agent can be spotted inthe liner byusing a string of tubing extending from the bottom of the liner to thesurface. The wellbore and tubing above the chemical agent can be lilledwith oil or saltwater to maintain pressure control when communicationbetween the formation and the wellbore is restored. Y

FIG. 5 of the drawing is a partial view of the wellbore of FIG. 4showing an alternate method for closing olf the lower end of the lineremployed in accordance with the invention. As indicated therein, theliner 30 may be simply a cylinder of suitablemetal open at the lowerend. Cement 33 may be placed'in the bottom of the wellbore about the endof the liner in order to close it. The use of cement as shown anchorsthe liner and prevents it from moving upwardly in the borehole when thefluid level therein is reduced by swabbing,

. In4 FIG. 6 of the drawing is shown a liner assembly consisting of aninner slotted liner 34 of alloy steel, ceramic material or the likewhich is resistant to heat and chemical attack and an outer sleeve 35 ofaluminum or a light metal whichcan be destroyed by chemical or thermalmeans. Thel slotted liner supports the outer sleeve against theformation pressure and thus permits the use of metals in the sleevewhich would otherwise be unsuitable because of their low strength atelevated temperatures. The width of the slots in the inner liner willdepend somewhatupon the particular metal employed in the sleeve. Ingeneral, slotsfrom about to about 1/2 inchin width will be satisfactory..If the outer sleeve and the slotted liner are made of metals havingsimilar coefficients of thermal expansion, they may be welded to oneanother as shown in the` drawing. In other cases, suitable collars andasbestos packing may be used to connect the two and accommodatedifferent rates of thermal expansion.

Casing 36 has been set and cemented in place in the wellbore shown inFIG. 6 of the drawing. The cement is designated by reference numeral377. Perforations 38 have been made opposite the unconsolidatedformation` The liner assembly is connected to production tubing 39 bycollar '4Q and is suspended adjacent the perforations. Packer 41 ofasbestos or other heat-resistant material is positioned between theproduction tubing and casing above the liner assembly. The packer is notalways essential, however, andin some cases can be dispensed with,particularly where the annular section of the wellbore is filled withgas and maintained under suliicient pressure to prevent the intlux offluids from the reservoir.

Heater .42 is lowered through production tubing 39 into the linerassembly shown in FIG. 6 in order to consolidate the formation. Uponcompletion of the coking operation, thel outer sleeve of the assemblycan be dissolved chemically'in the manner described heretofore, or itcan be melted by raising the temperature above the melting point of thematerial in the outer sleeve. The inner liner of the assembly remains inthe'borehole after the outer Vsleeve has been at least partiallydestroyed and, particularly in the case of the wells which are not casedopposite the producing zone, affords added protection against the influxof solids into the tubing with the producing uids should theconsolidated zones about the wellbore` subsequently fail,

FIG. 4 of the drawingillustrates a further method of carrying out theprocessV of the invention wherein a liner containing plugs ofa `fusibleor soluble metal is used. As shown in FIG. 7, liner 43 of steel or otherhigh melting, corrosion-resistant material contains slots or openingsiilled with plugs 44 of aluminum, magnesium, copper or other materialwhich can be readily melted or dissolved with acid or a causticsolution. A convenient method of fabricating the liner is to drill holesin a steel pipe and plug them with rivets of aluminum or the like. A capcan be welded or threaded onto the lower end of the pipe. The liner issupported in the wellbore by a packer or similar anchoring means 45which engages casing 46 above the unconsolidated producing zone. Thecement behind the casing is designated by reference numeral 47. Heater48gat the end of cable 49 is lowered into the liner in order to coke theformation and may be thereafter utilized to melt plugs 44 in the liner.An acid or base may instead beemployed to dissolve the plugs.

The invention is further illustrated by the results of tests carriedoutlto determine the electiveness of the process. In the first test, an18 API gravity Bayou Choctaw crude oil was coked in unconsolidated sandpacked around a 7-inch perforated cemented casing Vlor was filledwithcrudeoil and then blocked olf above the perforations. An electricalheater 3 inches in diamter and 10.8 feet long was positionedinside theliner'opposite the perforations and energized. A period of about 41/2hours was required to Vvaporizethe oil in the annular space and driveitthrough the perforations into the sand.

During this period the heater temperature, as Yindicated bythermocouples attached to its outer surface', gradually increased toabout 15920" F. The power to theV heater was thereafter decreased atintervals to maintain Va constant temperature. Heating was continued for24 Vhours formed.` It is therefore apparent that the processkof theinvention providesan effective means for 'overcoming the diicultiesencountered with unconsolidated sands in the n What is claimed is:` Yu 1. A process for consolidating an unconsolidated subterraneanformation surrounding a borehole which com-- prises installing animpermeable liner in said `boreholej after the oil in the wellbore hadbeen vaporized. The f heater was then turned off and the borehole wasallowed to'cool forseveral hours.

' The heater, liner and cemented'casingwere raised from the borehole andexamined; The sand surrounding the cemented liner had been coked for anaverage distance of about 11/2 inches away from the liner. Next totheliner it was well consolidated. The coked sand was found to have anaverage permeability to oil of about 10,154-millidarcies and anaverageperrneability to air of-about 16,123 millidarcies. the coked sandshowed an average strengthiof about 456 pounds per square inch. f Y

, After the above test had Vdemonstrated that the use of an electricalheater inside a liner is an eiectivemeans `for coking oil in anunconsolidated formation, tests Were carried out to determine .theeffectiveness of concentrated nitric acid for dissolving plugs of copperand brass 5/6 inch in diameter set in holes inV Vthe wall of steeltubing. The tubingv containing the plugs Vwasheated at 1200 F. for 24hours and thereafter filled with the acid. It was found that the acidate its wayV through the brass in about Y 20 minutes, while about 25minutes was required to dissolve the copper. v

The effect of acids and bases on coke formed by heat- Measure of thecompressive Ystrength of` to prevent uid communication between theborehole andV said unconsolidated formation, said'lin'er being `atleasttween saidbrehole and'sa'id formation.

, 2.V A process forrconsolidating an unconsolidated sub1 terranean4formation surrounding a borehole which cornprises installing animpermeable -liner in said ,borehole Y to preventrtiuid communicationbetween the borehole and n l-said unconsolidated formation, said linerbeing at leastj Y in part readily soluble in a selectedV chemicalreagent; low`.

y ering a Wel'lboreheater `into said liner adjacent said'ft'n`r` mation;heating Voilirr said formation bymeans of saidV heater untilsicient'coke to consolidate' said formation in the immediate vicinitysaid borehole has been"l formed; and thereafter introducing saidselected chernit'tal'4 f i. reagent into said borehole. in contact withsaid liner to at ing crude oil inthe presence of unconsolidated sandwasY tested by soaking samples of the coke in 28%'Y hydroi chloric acid,concentrated sodium hydroxide and concentrated nitric acid for periodsranging from 23 days to 35 days. Neither the acids nor the caustic hadany percep- Vtible effect `upon the coke. v

Therdata obtainedin the above-described' tests clearly demonstrate thatunconsolidated sands surrounding a wellbore can kbe consolidated byutilizing a heater inside a liner within the Wellbore to coke'oil Vincontact with the sands, that chemical reagents canbe employedto dissolvecopper and similar inserts in liners,VV 'and that the use ofsuchreagents doesY not adversely affect the coke thus least partiallydissolve said liner and thereby restore fluid communication between saidborehole and said formation.

3. A process as defined by claim 2 wherein said chemical reagentV is anacid.

4. A process as defined by Vclaim 2 wherein said chemical reagent is abase. Y

References Cited Yin thele of thisl patent Y Y UNITED STATES PATENTS v2,335,578 Carter Nov. 30,: 1943 V2,491,035 Akeyson et al. May 28,19.7463k Y 2,685,930 Aibaugh ...f f Aug. 10, 1954 2,906,340Y HerzogSept. 29, :11959 2,914,309 sa10m0nSSqn- Nov. 24, 1959; Y 3,003,555 YFreeman e V oet. 10, 1961V 3,072,188V Y

1. A PROCESS FOR CONSOLIDATING AN UNCONSOLIDATED SUBTERRANEAN FORMATIONSURROUNDING A BOREHOLE WHICH COMPRISES INSTALLING AN IMPERMEABLE LINERIN SAID BOREHOLE TO PREVENT FLUID COMMUNICATION BETWEEN THE BOREHOLD ANDSAID UNCONSOLIDATED FORMATION, SAID LINER BEING AT LEAST IN PART READILYFUSIBLE AT A TEMPERATURE IN EXCESS OF A PREDETERMINED COKINGTEMPERATURE; LOWERING A WELLBORE HEATER INTO SAID LINER ADJACENT SAIDFORMATION; HEATING OIL IN SAID FORMATION TO SAID COKING TEMPERATURE BYMEANS OF SAID HEATER UNTIL SUFFICIENT COKE TO CONSOLIDATE SAID FORMATIONIN THE IMMEDIATE VICINITY OF SAID BOREHOLE HAS BEEN FORMED; ANDTHEREAFTER INCREASING THE TEMPERATURE IN SAID BOREHOLE BY MEANS OF SAIDHEATER TO AT LEAST PARTIALLY FUSE SAID LINER AND THEREBY RESTORE FLUIDCOMMUNICATION BETWEEN SAID BOREHOLE AND SAID FORMATION.
 2. A PROCESS FORCONSOLIDATING AN UNCONSOLIDATED SUBTERRANEAN FORMATION SURROUNDING ABOREHOLE WHICH COMPRISES INSTALLING AN IMPERMEABLE LINER IN SAIDBOREHOLE TO PREVENT FLUID COMMUNICATION BETWEEN THE BOREHOLE AND SAIDUNCONSOLIDATED FORMATION, SAID LINER BEING AT LEAST IN PART READILYSOLUBLE IN A SELECTED CHEMICAL REAGENT; LOWERING A WELLBORE HEATER INTOSAID LINER ADJACENT SAID FORMATION; HEATING OIL IN SAID FORMATION BYMEANS OF SAID HEATER UNTIL SUFFICIENT COKE TO CONSOLIDATE SAID FORMATIONIN THE IMMEDIATE VICINITY OF SAID BOREHOLE HAS BEEN FORMED; ANDTHEREAFTER INTRODUCING SAID SELECTED CHEMICAL REAGENT INTO SAID BOREHOLEIN CONTACT WITH SAID LINER TO AT LEAST PARTIALLY DISSOLVE SAID LINER ANDTHEREBY RESTORE FLUID COMMUNICATION BETWEEN SAID BOREHOLE AND SAIDFORMATION.